The present invention relates to an apparatus for heating an object having a circular cross-section, and more particularly to such an apparatus for heating a CRT (cathode ray tube) neck and sealing a glass stem wafer or electron gun mount therein.
A CRT comprises three major glass sections, namely a panel, a funnel, and a neck. The neck comprises at its end remote from the panel an electron gun that is mounted on a glass wafer with lead wires for the gun electrodes projecting through the wafer.
During manufacture, the CRT is held in the vertical panel-up position of a "carrousel" and the wafer with the gun mounted thereon is upwardly inserted into the neck by a mount pin or socket. Heat from burners is then applied to the outside of the neck proximate the wafer, i.e. at the "seal plane", and the CRT and the wafer are rotated as they are indexed to various stationary fire positions around the carrousel. The fires are positioned around the vertical central axis of the CRT neck so that the neck softens, thins, and then seals to the wafer. Also, excess neck material that is lower than the wafer (cullet) is cut off and therefore falls away from the neck.
Presently, there is a trend towards larger CRTs. This means that the carrousel and the rotating machinery, including two vertical support bars for the CRT, must be relatively large and heavy, and therefore expensive. Further, the two vertical bars interfere with the placement of an electrical resistance oven around the CRT neck for a preferred preheat step before the wafer sealing operation and an annealing step after sealing. Thus additional burners are required to perform these steps instead of the resistance oven. This requires additional carrousel positions and the heating provided by the burners is not as uniform as that provided by the resistance oven. The present invention overcomes the above problems.